TGF-β's (transforming growth factor-β's) activate fibrotic and tumor-promoting signaling cascades. Three mammalian TGFβ's, TGFβ1, TGFβ2, and TGFβ3, can activate the TGFβ pathway. The TGFβ's bind to and signal through cell surface receptors (see Singh et al. (2004) Curr. Opin. Drug Disc. and Dev., 7: 437-445). A TGFβ first binds to a type II receptor (TpRII), which then binds to and phosphorylates a type I receptor (TβRI) (i.e., an activin receptor-like kinase (ALK)). There is a family of ALK proteins including ALK-5, which is the most specific ALK for TGFβ. Activation of ALK-5 leads to phosphorylation of intracellular proteins, which results in the regulation of fibrosis and tumorigenesis. Therefore, the discovery of ALK-5 inhibitors is an active area of investigation to discover inhibitors to treat cancer, and conditions involving fibrosis (see Singh et al. (2004)).
One example of a condition that involves fibrosis is the formation of scars during wound repair. Scars, including hypertrophic and keloid scars, typically result from the deposition of collagen at wound sites. Wounds may be produced through many different kinds of mechanisms including surgery, accidental injuries, burns, trauma, etc. It has been reported that the application of TGFβ3, antibodies to TGFβ1 and TGFβ2 which inhibit the TGFβ pathway can assist in reducing scarring (O'Kane and Ferguson, (1997) Int. J. Biochem. Cell Biol., 29: 63-78). Accordingly, there is an ongoing need in the art for small molecule ALK-5 inhibitors that can be used to reduce scar formation, and for the treatment of other fibrotic conditions, as well as cancer.